Blender for Previs/Layout
Well, blender.stackexchange focuses around usage oriented questions, specific tasks etc, not opinion based, open questions about the market place.

But the answer is: Yes, there are people doing that. At the Blender Conference 2018 was a talk from someone working at Lucasfilm:

https://www.youtube.com/watch?v=UpcKPJTmqSI
(Blender Workflow for Feature Films - Jama Jurabaev)

Grease Pencil is a beast.

https://blenderartists.org/ might be a better place to have a discussion